• Korean Journal of Metals and Materials
• /
• v.48 no.8
• /
• pp.741-748
• /
• 2010

We studied the corrosion and oxidation properties of Fe-18Cr-0.4Nb-(0.1~0.6)Ti-(1~3)Si-(0.5~2)Mo stainless steel. The resistance to general and pitting corrosion was evaluated and the results were analyzed by Response Surface Methodology (RSM) as a function of alloy composition. The effects of alloy composition and heat treatment on the oxidation resistance were also examined. Mo increased both general corrosion resistance and pitting corrosion resistance. Si improved the resistance of the alloys to pitting corrosion. Si was also beneficial for general corrosion resistance of the alloys containing Mo at more than 1 wt.%. However, Mo was detrimental when its content was lower. Effects of Ti on general corrosion properties appeared to be weak and a high concentration of Ti appeared to deteriorate pitting resistance. The thickness of the oxidation scale increased and adhesion of the scale worsened as the temperature increased from $800^{\circ}C$ to $900^{\circ}C$. Weight gain of the alloys due to oxidation at $900^{\circ}C$ clearly showed that the resistance to oxidation is improved by annealing at $860^{\circ}C$ and an increase of Si content.

• Journal of the Korean Society for Heat Treatment
• /
• v.19 no.2
• /
• pp.90-95
• /
• 2006

Nitriding or carburizing of carbon steels results in good mechanical properties such as high surface hardness and wear resistance but it has no affection on the corrosion resistance. Corrosion properties of nitriding and carburizing steels could be deteriorated. So, recently, there have been great demand for oxi-nitriding to enhance both mechanical properties and corrosion resistance. In this study, the corrosion resistance of carbon steel, S35C, and free cutting steel, SUM222, are prepared by vacuum nitriding and vacuum post-oxidation were compared with those treated by nitriding. After vacuum post-oxidation, $5{\mu}m$ oxide layer was formed on the nitride layer with $20{\sim}30{\mu}m$ depth. Potentio-dynamic polarization curve in corrosion test showed that the corrosion potential after post oxidation was increased from 200 mV to 800 mV in S35C and from 600 mV to 1200 mV in SUM222. SEM analyses showed that pores was increased and surface roughness became rougher with post oxidation. However, the formation of $Fe_3O_4$ resulted in the enhanced corrosion resistance of steels.

• Korean Journal of Materials Research
• /
• v.12 no.8
• /
• pp.676-681
• /
• 2002

Microstructure, mechanical properties, and oxidation resistance of TiAIN thin films deposited on quenched and tempered STD61 tool steel by arc ion plating were studied using XRD, XPS and micro-balance. The TiAIN film was grown with the (200) orientation. The grain size of TiAIN thin film decreased with increasing Al contents, while chemical binding energy increased with Al contents. When hard coating films were oxidized at $850^{\circ}C$ in air, oxidation resistance of both TiN and TiCN films became relatively lower since the surface of films formed non-protective film such as $TiO_2$. However, oxidation resistance of TiAIN film was excellent because its surface formed protective layer such as $_A12$$O_3$ and $_Al2$$Ti_{7}$$O_{15}$, which suppressed oxygen intrusion.

• Journal of the Korean institute of surface engineering
• /
• v.29 no.6
• /
• pp.607-614
• /
• 1996

Yttrium(Y) coating was incorporated by ion-plating method either directly on the TiAl substrate or after pack aluminizing on TiAl to improve the oxidation resistance of TiAl alloy. After Y-coating, heat treatment at low oxygen partial pressure was carried out. Performance of various coating was evaluated by isothermal and cyclic oxidation tests. A simple Y-coating without pack aluminizing can give a detrimental effect on the. oxidation resistance of TiAl alloy, because it enhances formation of $TiO_2$. On the other hand, a composite coating of aluminide-yttrium has shown excellent oxidation resistance. A continuous protective $Al_2O_3$ scale is formed on the aluminized TiAl, and Y-coating improves $Al_2O_3$ scale adherence and substantially prevents depletion of Al in the aluminide-coating layer.

• Corrosion Science and Technology
• /
• v.7 no.4
• /
• pp.233-236
• /
• 2008

Halide-activated pack cementation was utilized to deposit B-doped silicide coating. The pack powders were consisted of $3Wt.c/oNH_4Cl$, 7Wt.c/oSi, $90Wt.c/oAl_2O_3+TiB_2$. B-doped silicide coating was consisted of two layers, an outer layer of $NbSi_2$ and an inner layer of $Nb_5Si_3$. Isothermal oxidation resistance of B-doped silicide coating was tested at $1250^{\circ}C$ in static air. B-doped silicide coating had excellent oxidation resistance, because continuous $SiO_2$ scale which serves as obstacle of oxygen diffusion was formed after oxidation.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.171-171
• /
• 2010

In this work, we investigated the effect of the oxidation temperature on the unipolar and bipolar resistance switching behaviors of the oxidized TiO-x films. TiOx films on Pt electrodes were fabricated by the oxidation of Ti films at $550^{\circ}C$ for 1 to 3 hours. The unipolar and bipolar resistance switching properties were investigated with the oxidation temperature and time. Also, the crystal structure and the physical properties such as chemical bonding states of TiOx layers were characterized in addition to the resistance switching characteristics. The resistance switching behaviors of TiOx films oxidized at above $450^{\circ}C$ and below $650^{\circ}C$ was shown. So, we investigated that the resistance switching behaviors of TiOx films oxidized at $550^{\circ}C$ with the oxidation time from 1 to 3 hour. The memory windows of unipolar switching in the oxidized TiOx films were reduced with increasing the oxidation time, but those of the bipolar switching were slightly enlarged. The enlargement of rutile TiO2 peak with increasing the oxidation time and temperature was studied by X-ray diffraction. An increase of non-lattice oxygen and Ti3+ in the TiOx films with the oxidation times was investigated by X-ray photoemission spectroscopy. It was expected that the uipolar and bipolar resistive switching of the oxidized TiOx film was strongly related with the migration of non-lattice oxygen anions and schottky barrier height, respectively.

• Journal of the Korean Society for Heat Treatment
• /
• v.22 no.5
• /
• pp.298-306
• /
• 2009

Gas nitriding and post oxidation were performed on stainless steels and SACM 645 steel. With increasing gas nitriding time, the increasing rate of nitrided layer was most rapid on SACM 645 steel and the nitriding depth of nitrided layer was most narrow on STS 304 steel among three steels. Corrosion resistance was increased with post oxidation on stainless steels and with increasing time the effect of corrosion resistance was decreased to compare with relatively short gas nitriding time. An improvement effect of corrosion resistance was consisted of predominantly on austenitic stainless steel by post oxidation after gas nitriding among three steels and it was relatively less influenced on martensitic stainless steel.

• Journal of Power System Engineering
• /
• v.10 no.3
• /
• pp.51-57
• /
• 2006

The effect of grain size on corrosion resistance and high temperature oxidation behavior was studied in 22Cr-15Ni-5W super austenitic stainless steels for desulfurization equipment as a heat power station. In the high temperature oxidation test, oxidation rate was increased as the temperature increased from $600^{\circ}C\;to\;800^{\circ}C$. In vapor, oxidation rate was faster than that in air. Because the vapor was inhibited nucleation of $Cr_2O_3$ film. And the high temperature oxidation resistance at $600^{\circ}C{\sim}800^{\circ}C$ was excellent from all specimens and specimen of the smallest grain size was the most excellent. Because increasing of diffusion course through the grain-boundary was promoted nucleation and growth of $Cr_2O_3$ film. In the test temperature at $600^{\circ}C{\sim}800^{\circ}C$, Cr rich round particle oxide was formed in air, whereas Fe rich needle type oxide was developed in vapor.

• Journal of the Korean institute of surface engineering
• /
• v.28 no.3
• /
• pp.142-151
• /
• 1995

In this research, a thin layer of Cr was coated on the pure Ni and Inconel 601 by PECVD (Plasma Enhanced Chemical Vapor Deposition) in order to study the effect of Cr on the oxidation behavior at high temperature. Cr coated Inconel 601, which was oxidized at $1100^{\circ}C$ for 24 hours, formed a protective $Cr_2O_3$ oxide layer and the resistance to isothermai oxidation was improved. On the other hand, oxidation resistance of Cr coated Inconel 601 at 100$0^{\circ}C$ was not significantly improved, probably due to the formation or insufficient $Cr_2O_3$ layer. But, when oxidized at $1000^{\circ}C$ and $1100^{\circ}C$ for 100 hours, Cr coated Inconel 601 improved isothermal oxidation resistance by the formation of continuous $Cr_2O_3$ external scale and by the development of $Al_2O_3$ subscales. Cr coated Ni formed inner layer of $Cr_2O_3$ within almost pure NiO, which provided additional cation vacancies, thus increasing the mobility of Ni ions in this region. It is believed that this doping effect resulted in an increase in the observed oxidation rate compared with pure Ni and did not improve the oxidation resistance.

• Progress in Superconductivity and Cryogenics
• /
• v.24 no.4
• /
• pp.40-45
• /
• 2022

The electrical/thermal stabilities and magnetic field controllability of a no-insulation (NI) high-temperature superconducting magnet are characterized by contact resistance between turn-to-turn layers, and the contact resistance characteristics are determined by properties of conductor surface and winding tension. In order to accurately predict the electromagnetic characteristics of the NI coil in a design stage, it is necessary to control the contact resistance characteristics within the design target parameters. In this paper, the contact resistance and critical current characteristics of a rare-earth barium copper oxide (REBCO) conductor were measured to analyze the effects of surface treatment conditions (roughness and oxidation level) of the copper stabilizer layer in REBCO conductor. The test samples with different surface roughness and oxidation levels were fabricated and conductor surface analysis was performed using scanning electron microscope, alpha step surface profiler and energy dispersive X-ray spectroscopy. Moreover, the contact resistance and critical current characteristics of the samples were measured using the four-terminal method in a liquid nitrogen impregnated cooling environment. Compared with as-received REBCO conductor sample, the contact resistance values of the REBCO conductors, which were post-treated by the scratch and oxidation of the surface of the copper stabilizer layer, tended to increase, and the critical current values were decreased under certain roughness and oxidation conditions.